U.S. patent application number 15/806885 was filed with the patent office on 2018-05-31 for pneumatic tire.
This patent application is currently assigned to Toyo Tire & Rubber Co., Ltd.. The applicant listed for this patent is Toyo Tire & Rubber Co., Ltd.. Invention is credited to Hisashi Takahashi.
Application Number | 20180147891 15/806885 |
Document ID | / |
Family ID | 60269598 |
Filed Date | 2018-05-31 |
United States Patent
Application |
20180147891 |
Kind Code |
A1 |
Takahashi; Hisashi |
May 31, 2018 |
PNEUMATIC TIRE
Abstract
Provided is a pneumatic tire including: a plurality of land
portion rows formed by arranging a plurality of land portions
formed by main grooves and transverse grooves in a tire
circumferential direction on a tire tread portion, wherein assuming
a tire circumferential length of an element formed of the land
portion and the transverse groove disposed adjacently to the land
portion on one side in the circumferential direction as a pitch
length P and the number of pitches which is the number of the
elements over the whole circumference of the tire as N, the number
of kinds k of pitch lengths P in the circumferential direction is
set to N/4 or more and N or less. Assuming the pitch lengths P in a
descending order as P.sub.1, P.sub.2, . . . , P.sub.k, a
relationship of P.sub.m-1/P.sub.m<1.050 and a relationship of
1.60.ltoreq.P.sub.1/P.sub.k<2.00 are satisfied (m: an integer of
2 to k).
Inventors: |
Takahashi; Hisashi;
(Itami-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Toyo Tire & Rubber Co., Ltd. |
Itami-shi |
|
JP |
|
|
Assignee: |
Toyo Tire & Rubber Co.,
Ltd.
Itami-shi
JP
|
Family ID: |
60269598 |
Appl. No.: |
15/806885 |
Filed: |
November 8, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B60C 11/0306 20130101;
B60C 11/0318 20130101 |
International
Class: |
B60C 11/03 20060101
B60C011/03 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 28, 2016 |
JP |
2016-230239 |
Nov 28, 2016 |
JP |
2016-230246 |
Claims
1. A pneumatic tire comprising a tire tread portion comprising: a
plurality of main grooves extending in a tire circumferential
direction; a plurality of transverse grooves extending in a
direction which intersects with the main grooves; a plurality of
land portion rows formed by arranging a plurality of land portions
formed by the main grooves and the transverse grooves in the tire
circumferential direction, wherein at least one land portion row is
formed such that assuming a tire circumferential length of an
element formed of each land portion and the transverse groove
disposed adjacently to said each land portion on one side in the
tire circumferential direction as a pitch length and the number of
pitches which is the number of the elements over the whole
circumference of the tire as N, the number of kinds k of pitch
lengths in the tire circumferential direction is set to N/4 or more
and N or less, and assuming the pitch lengths in a descending order
as P.sub.1, P.sub.2, . . . , P.sub.k and m as an integer of 2 to k,
a relationship of P.sub.m-1/P.sub.m<1.050 and a relationship of
1.60.ltoreq.P.sub.1/P.sub.k<2.00 are satisfied.
2. The pneumatic tire according to claim 1, wherein at least one
land portion row is formed such that a maximum value of a pitch
length ratio of the elements disposed adjacently to each other in
the tire circumferential direction is less than 1.71.
3. The pneumatic tire according to claim 1, wherein in the
plurality of respective land portion rows formed on the tire tread
portion, the number of kinds k of the pitch lengths in the tire
circumferential direction is set to N/4 or more and N or less, and
a relationship of P.sub.m-1/P.sub.m<1.050 and a relationship of
1.60.ltoreq.P.sub.1/P.sub.2<2.00 are satisfied.
4. The pneumatic tire according to claim 3, wherein at least one
land portion row out of the plurality of land portion rows differs
from the other land portion rows in arrangement of the elements
having plural kinds of pitch lengths.
5. The pneumatic tire according to claim 3, wherein at least one
land portion row out of the plurality of land portion rows differs
from the other land portion rows in phase of the elements in the
tire circumferential direction.
6. The pneumatic tire according to claim 3, wherein at least one
land portion row out of the plurality of land portion rows differs
from the other land portion rows in the number of pitches.
7. A pneumatic tire comprising a tire tread portion comprising: a
plurality of main grooves extending in a tire circumferential
direction; a plurality of transverse grooves extending in a
direction which intersects with the main grooves; a plurality of
land portion rows formed by arranging a plurality of land portions
formed by the main grooves and the transverse grooves in the tire
circumferential direction, wherein assuming a tire circumferential
length of an element formed of each land portion and the transverse
groove disposed adjacently to said each land portion on one side in
the tire circumferential direction as a pitch length, the number of
pitches which is the number of the elements in each land portion
row over the whole circumference of the tire as N, and the number
of land portion rows as L, each land portion row includes the
elements having plural kinds of pitch lengths, and at least one
land portion row includes the elements which differ in pitch length
from the elements of other land portion rows, and the number of
kinds j of pitch lengths over the whole tire tread portion is set
to N/4 or more and N.times.L or less, and assuming the pitch
lengths over the whole tire tread portion in a descending order as
P.sub.1, P.sub.2, . . . , P.sub.j and t as an integer of 2 to j, a
relationship of P.sub.t-1/P.sub.t<1.050 and a relationship of
1.60.ltoreq.P.sub.1/P.sub.j<2.00 are satisfied.
8. The pneumatic tire according to claim 7, wherein in each land
portion row, a maximum value of a pitch length ratio of the
elements disposed adjacently to each other in the tire
circumferential direction is less than 1.71.
9. The pneumatic tire according to claim 7, wherein the number of
kind j of pitch lengths over the whole tire tread portion is set to
N.times.L/4 or more and N.times.L or less.
10. The pneumatic tire according to claim 7, wherein at least one
land portion row out of the plurality of land portion rows differs
from the other land portion rows in phase of the elements in the
tire circumferential direction.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is based upon and claims the benefit of
priority from the prior Japanese Patent Applications No.
2016-230239 and 2016-230246, filed on Nov. 28, 2016; the entire
contents of which are incorporated herein by reference.
BACKGROUND
1. Field of the Invention
[0002] The disclosure of the present invention relates to a
pneumatic tire.
2. Description of the Related Art
[0003] As one of noises which a tire generates, there has been
known a striking sound which is generated when a tread portion
strikes a road surface at the time of coming into contact with a
ground. When a timing at which a ground contact shape of the tire
at the time of coming into contact with a road surface and a tread
pattern of the tire agree with each other is fixed during a kick-in
operation or a kick-out operation of the tire, a peak of the
striking sound becomes conspicuous. For example, when a pitch
length of a tread pattern in a tire circumferential direction is
fixed, a peak of pitch noises becomes high. Further, noises
generated by a tire include an air column tube resonance sound
generated by an air column formed between a main groove formed on a
tread portion and a road surface, and a noise level is increased
when a frequency of the pitch noise and a frequency of the air
column tube resonance at a specific speed agree with each
other.
[0004] Conventionally, there has been known a tire where pitch
variations are adopted in a tread pattern for reducing pitch noises
(see US 2015/0375571A1, JP-A-2014-221573, JP-A-2000-043507).
However, in the conventional pitch variable arrangement, the number
of kinds of pitch lengths (that is, variable numbers) in a tire
circumferential direction are usually set to 3 kinds or 5 kinds.
Accordingly, it is not safe to say that such pitch variable
arrangement has a sufficient effect of lowering a peak of pitch
noises.
[0005] The present invention has been made in view of such
circumstances, and it is an object of the present invention to
provide a pneumatic tire which can lower a peak of pitch noises by
dispersing frequencies of the pitch noises thus lowering a noise
level.
SUMMARY
[0006] A pneumatic tire according to a first embodiment of the
present invention has a tire tread portion which includes: a
plurality of main grooves extending in a tire circumferential
direction; a plurality of transverse grooves extending in a
direction which intersects with the main grooves; a plurality of
land portion rows formed by arranging a plurality of land portions
formed by the main grooves and the transverse grooves in the tire
circumferential direction. At least one land portion row is formed
such that assuming a tire circumferential length of an element
formed of each land portion and the transverse groove disposed
adjacently to said each land portion on one side in the tire
circumferential direction as a pitch length and the number of
pitches which is the number of the elements over the whole
circumference of the tire as N, the number of kinds k of pitch
lengths in the tire circumferential direction is set to N/4 or more
and N or less, and assuming the pitch lengths in a descending order
as P.sub.1, P.sub.2, . . . , P.sub.k and m as an integer of 2 to k,
a relationship of P.sub.m-1/P.sub.m<1.050 and a relationship of
1.60.ltoreq.P.sub.1/P.sub.k<2.00 are satisfied.
[0007] In the first embodiment, the above-mentioned at least one
land portion row may be formed such that a maximum value of a pitch
length ratio of the elements disposed adjacently to each other in
the tire circumferential direction may be less than 1.71. In the
plurality of respective land portion rows formed on the tire tread
portion, the number of kinds k of pitch lengths in the tire
circumferential direction may be set to N/4 or more and N or less,
and a relationship of P.sub.m-1/P.sub.m<1.050 and a relationship
of 1.60.ltoreq.P.sub.1/P.sub.k<2.00 may be satisfied.
[0008] A pneumatic tire according to a second embodiment of the
present invention has a tire tread portion which includes: a
plurality of main grooves extending in a tire circumferential
direction; a plurality of transverse grooves extending in a
direction which intersects with the main grooves; a plurality of
land portion rows formed by arranging a plurality of land portions
formed by the main grooves and the transverse grooves in the tire
circumferential direction. Assuming a tire circumferential length
of an element formed of each land portion and the transverse groove
disposed adjacently to said each land portion on one side in the
tire circumferential direction as a pitch length, the number of
pitches which is the number of the elements in each land portion
row over the whole circumference of the tire as N, and the number
of land portion rows as L, each land portion row includes the
elements having plural kinds of pitch lengths, and at least one
land portion row has the elements having pitch lengths different
from pitch lengths of other land portion rows. Further, the number
of kinds j of pitch lengths over the whole tire tread portion are
set to N/4 or more and N.times.L or less, and assuming the pitch
lengths over the whole tire tread portion in a descending order as
P.sub.1, P.sub.2, . . . , P.sub.j and t as an integer of 2 to j, a
relationship of P.sub.t-1/P.sub.t<1.050 and a relationship of
1.60.ltoreq.P.sub.1/P.sub.j<2.00 are satisfied.
[0009] In the second embodiment, in each land portion row, a
maximum value of a pitch length ratio of the elements disposed
adjacently to each other in the tire circumferential direction may
be less than 1.71.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a developed view of a tread pattern of a pneumatic
tire according to one embodiment;
[0011] FIG. 2 is a partially enlarged view of a tread pattern
according to a first embodiment;
[0012] FIG. 3 is a graph showing a result of frequency analysis in
area variation with respect to the first embodiment;
[0013] FIG. 4 is a partially enlarged view of a tread pattern
according to a second embodiment;
[0014] FIG. 5A to FIG. 5E are partially enlarged views respectively
showing a pitch variable arrangement of each land portion row in
the tread pattern according to the second embodiment; and
[0015] FIG. 6 is a graph showing a result of frequency analysis in
area variation with respect to the second embodiment.
DETAILED DESCRIPTION
[0016] In the conventional pitch variable arrangement, to further
lower a peak of pitch noises, it is effective to disperse
frequencies of pitch noises. For this end, it is effective to
increase the variable numbers (that is, the number of kinds of
pitch lengths) compared to that of the conventional pitch variable
arrangement, and it is also effective to increase a variable ratio
(that is, a ratio of a maximum pitch length to a minimum pitch
length). In this case, when the variable ratio is excessively
large, an n-order component and a 2n-order component of the noise
pitch agree with each other thus generating large noises.
Accordingly, for lowering a noise level, it is advantageous to set
large variable numbers while setting a large variable ratio within
a range that an n-order component and a 2n-order component of the
noise pitch do not agree with each other.
[0017] The present embodiment has been made in view of such
finding, and it is an object of the present embodiment to provide a
pneumatic tire which can further lower a noise level compared to a
pneumatic tire having a conventional pitch variable arrangement.
That is, according to the present embodiment, a peak of pitch
noises can be lowered by dispersing frequencies of the pitch noises
thus lowering a noise level. By lowering the peak of the pitch
noises, a noise level when a frequency of the pitch noise and a
frequency of an air column tube resonance agree with each other can
be also lowered.
[0018] Hereinafter, embodiments are described with reference to
drawings.
First Embodiment
[0019] FIG. 1 is a developed view of a tread portion of a pneumatic
tire according to one embodiment showing a tread pattern over the
whole circumference of the tire, and FIG. 2 is a partially enlarged
view of the tread pattern. As shown in FIG. 1 and FIG. 2, on a
surface (that is, a surface which is brought into contact with a
road surface during traveling) of a tread portion 10 which is made
of tread rubber, a plurality of main grooves 12 extending in a tire
circumferential direction CD, a plurality of transverse grooves 14
extending in a direction which intersects with the main grooves 12,
and a plurality of land portion rows 18 each of which is formed by
arranging a plurality of land portions 16 formed by the main
grooves 12 and the transverse grooves 14 in the tire
circumferential direction CD are formed. With respect to the
configurations of the pneumatic tire other than the tread pattern,
known tire configurations are applicable and hence, other
configurations of the pneumatic tire are not particularly
limited.
[0020] In this embodiment, four main grooves 12 are formed on the
tread portion at intervals in a tire width direction WD. That is,
the main grooves 12 are formed of: a pair of left and right center
main grooves 12A, 12A which is positioned at a center portion of
the tread portion in the tire width direction WD with a tire
equator CL sandwiched therebetween; and a pair of left and right
shoulder main grooves 12B, 12B which is disposed on both sides of
the pair of left and right center main grooves 12A, 12A. Each of
the four main grooves 12 is a straight groove extending parallel to
the tire circumferential direction CD.
[0021] In this embodiment, the transverse grooves 14 are grooves
extending in a direction which intersects with the main grooves 12
and crossing the respective land portion rows 18. Accordingly, the
land portions 16 are formed as blocks divided by the transverse
grooves 14 in the tire circumferential direction CD. The transverse
grooves 14 may not be disposed parallel to the tire width direction
WD provided that the transverse grooves 14 are grooves extending in
the tire width direction WD. That is, the transverse grooves 14 may
be grooves extending in the tire width direction WD while being
inclined with respect to the tire width direction WD.
[0022] On the tread portion 10, five land portion rows 18 are
defined by the main grooves 12 in the tire width direction WD. That
is, the land portion rows 18 are formed of: a center land portion
row 18C which is sandwiched between the pair of center main grooves
12A, 12A; a pair of left and right shoulder land portion rows 18S,
18S which is positioned outside the pair of shoulder main grooves
12B, 12B in the tire width direction WD respectively; and a pair of
left and right mediate land portion rows 18M, 18M each of which is
sandwiched between the center main groove 12A and the shoulder main
groove 12B. The large number of transverse grooves 14 are formed at
intervals in the tire circumferential direction CD. Accordingly,
each of the land portion rows 18 is formed as a block row where the
land portions 16 which are the plurality of blocks are arranged in
a row in the tire circumferential direction CD.
[0023] In this embodiment, in the above-mentioned five land portion
rows 18, by imparting a plurality of different pitch lengths P to
repetitive elements 20 each of which is formed of the land portion
16 and the transverse groove 14, land portion rows each having a
pitch variable arrangement are formed.
[0024] To be more specific, in each land portion row 18, assuming
the number of pitches over the whole circumference of the tire as
N, the number of kinds k of pitch lengths P (that is, variable
number) in the tire circumferential direction CD is set to N/4 or
more and N or less (N/4.ltoreq.k.ltoreq.N). The number of kinds k
of the pitch lengths P is set to N/4 or more and hence, frequencies
of pitch noises are dispersed so that an effect of lowering a noise
level can be enhanced. From a viewpoint of such a noise level
lowering effect, it is preferable that the number of kinds k of the
pitch lengths P be as many as possible. Accordingly, it is
preferable that the number of kinds k be N/2 or more, and it is
more preferable that the pitch length P be changed with respect to
all elements 20, that is, k=N.
[0025] As shown in FIG. 2, the pitch length P is a tire
circumferential length of the element 20 formed of each land
portion 16 and the transverse groove 14 disposed adjacently to the
land portion 16 on one side in the tire circumferential direction
CD. The element 20 is a repetitive unit (1 pitch) used for forming
the land portion row 18. Accordingly, each land portion row 18 is
formed by arranging the elements 20 having plural kinds of pitch
lengths P in the tire circumferential direction CD.
[0026] The number of pitches N over the whole circumference of the
tire is the number of the above-mentioned elements 20 over the
whole circumference of the tire, and is the number of elements
arranged over the whole circumference in the tire circumferential
direction CD in each land portion row 18. The number of pitches N
is not particularly limited, for example, the number of pitches N
may be 30 to 100, or may be 40 to 80. In the example shown in FIG.
1 and FIG. 2, the five land portion rows 18 have the same number of
pitches N, that is, the number of pitches N are respectively set to
56 (N=56).
[0027] In the example shown in FIG. 1 and FIG. 2, the pitch length
P is changed with respect to all elements 20 in the tire
circumferential direction CD, that is, the number of kinds k of the
pitch lengths P are set equal to the number of pitches N (k=N). To
explain this by taking the left shoulder land portion row 18S shown
in FIG. 2 as an example, all pitch lengths Pa.sub.1, Pa.sub.2,
Pa.sub.3, . . . , Pa.sub.N-1, and Pa.sub.N of the respective
elements 20 in the tire circumferential direction CD are set
different from each other.
[0028] In this embodiment, in each of five land portion rows 18,
assuming the number of kinds of the pitch lengths P as k and the
pitch lengths P in a descending order as P.sub.1, P.sub.2, . . . ,
P.sub.k, a relationship of P.sub.m-1/P.sub.m<1.050 and a
relationship of 1.60.ltoreq.P.sub.1/P.sub.k<2.00 are established
(in this relationship, m being an integer of 2 to k).
[0029] In this manner, by setting a variable ratio P.sub.1/P.sub.k
which is a ratio of a maximum pitch length P.sub.1 to a minimum
pitch length P.sub.k to less than 2.00, it is possible to suppress
the occurrence of a phenomenon that an n-order component and a
2n-order component of the noise pitch agree with each other thus
generating large noises. Further, by setting the variable ratio
P.sub.1/P.sub.k to 1.60 or more, the dispersion of frequencies of
pitch noises can be accelerated. The variable ratio P.sub.1/P.sub.k
is preferably set to 1.80 or more, is more preferably set to 1.90
or more and 1.98 or less.
[0030] By setting a maximum value of the pitch length ratio
P.sub.m-1/P.sub.m to less than 1.050, an effect of dispersing
frequencies of the pitch noises can be enhanced in cooperation with
the setting of the variable number and the setting of the variable
ratio described above. That is, the setting the maximum value of
the pitch length ratio P.sub.m-1/P.sub.m to a small value under a
condition that a large variable number is set and a high variable
ratio is set as described above leads to the elimination of
excessive irregularities in an increment of a pitch length from a
minimum pitch length P.sub.k to a maximum pitch length P.sub.1.
Accordingly, by dispersing the frequencies of the pitch noises
widely and uniformly, an effect of lowering a peak of pitch noise
can be enhanced. The pitch length ratio P.sub.m-1/P.sub.m is
preferably set to 1.040 or less (that is,
P.sub.m-1/P.sub.m.ltoreq.1.040), and the pitch length ratio
P.sub.m-1/P.sub.m is preferably set to 1.010 or more (that is,
P.sub.m-1/P.sub.m.gtoreq.1.010).
[0031] In this embodiment, an upper limit (that is, a maximum
value) of a pitch length ratio of the elements 20 disposed
adjacently to each other in the tire circumferential direction CD
is preferably set to less than 1.71. That is, out of two elements
20 disposed adjacently to each other in the tire circumferential
direction CD, assuming a pitch length of the element 20A having a
larger pitch length as P.sub.L and a pitch length of the element
20B having a smaller pitch length as P.sub.S, it is preferable that
an upper limit of a pitch length ratio expressed by P.sub.L/P.sub.S
be less than 1.71 (P.sub.L/P.sub.S<1.71). By defining an upper
limit of the pitch length ratio P.sub.L/P.sub.S of the elements 20
disposed adjacently to each other in the tire circumferential
direction CD as described above, it is possible to suppress
non-uniform wear caused by a rapid change in rigidity of the land
portion 16. From a viewpoint of non-uniform wear resistance, a
maximum value of the pitch length ratio P.sub.L/P.sub.S is further
preferably set to less than 1.34 (that is,
P.sub.L/P.sub.S<1.34).
[0032] The arrangement (that is, an arranging method) of the
elements 20 having plural kinds k of pitch lengths P is not
particularly limited. For example, when the number of kinds k is
equal to the number of pitches N (k=N), the elements 20 may be
arranged such that the pitch lengths P are gradually increased in
the tire circumferential direction CD. Alternatively, the elements
20 may be arranged such that the elements 20 having plural kinds k
of pitch lengths P are divided into three groups, that is, a large
pitch length group, a middle pitch length group and a small pitch
length group in a descending order from the elements 20 having the
larger pitch length P, and the elements are arranged in the tire
circumferential direction CD by selecting the elements from the
respective groups such that the elements belonging to the large
pitch length group and the elements belonging to the small pitch
length group are not disposed adjacently to each other. With such a
configuration, the elements 20 can be arranged in the tire
circumferential direction CD while suppressing the pitch length
ratio P.sub.L/P.sub.S of the elements 20 disposed adjacently to
each other to a small value.
[0033] As one example, in the example shown in FIG. 1 (k=N), from
the large pitch length group, the middle pitch length group and the
small pitch length group, a plurality of elements are allocated in
the tire circumferential direction CD in the order of the elements
having a large pitch length, the elements having a middle pitch
length, the elements having a small pitch length, the elements
having a middle pitch length, the elements having a large pitch
length, the elements having a middle pitch length, the elements
having a small pitch length, the elements having a middle pitch
length, the elements having a large pitch length, the elements
having a middle pitch length, the elements having a small pitch
length, and the elements having a middle pitch length thus
arranging the elements such that the pitch lengths of the elements
are smoothly changed in the tire circumferential direction CD. That
is, in an arrangement of the elements over the whole circumference
of the tire, the elements are arranged such that a group of a
plurality of elements belonging to the large pitch length group is
disposed at three positions over the circumference, and a group of
a plurality of elements belonging to the small pitch length group
is disposed between the groups of plurality of elements belonging
to the large pitch length group while interposing a group of a
plurality of elements belonging to the middle pitch length group
between the group of the plurality of elements belonging to the
large pitch length group and the group of the plurality of elements
belonging to the small pitch length group.
[0034] According to this embodiment, as described above, the large
variable number is set while setting the large variable ratio
within a range that an n-order component and a 2n-order component
of the noise pitch do not agree with each other and hence,
frequencies of pitch noises are dispersed so that a peak of pitch
noises can be lowered. Further, by lowering the peak of the pitch
noises, even when a frequency of the pitch noise and a frequency of
an air column tube resonance agree with each other, the increase of
a noise level can be suppressed. Accordingly, a noise level can be
more effectively lowered than ever before.
[0035] FIG. 3 is a graph showing a result of frequency analysis in
area variation with respect to a 56-pitch variable arrangement
which is adopted as one example of pitch variable arrangement in
the first embodiment, and an equal-pitch variable arrangement and a
3-pitch variable arrangement which are adopted as comparison
examples. The analysis is performed in accordance with a method
described in JP-A-2003-136926, the entire contents of which are
incorporated herein by reference. In the method, variable data on
ground contact area is acquired by scanning a ground contact
pattern of a tire with a road surface in the circumferential
direction of the tread pattern, and data on an area variation level
with respect to frequency is acquired by performing frequency
analysis based on such variation data. The tire size is set to
265/65R17, and a traveling speed is set to 80 km/h. The tire
pattern is set such that, in the 56-pitch variable arrangement,
pitch lengths are changed at an increment of 0.52 mm within a range
of from 29.10 mm to 57.68 mm. In the 3-pitch variable arrangement,
pitch lengths are set to 3 kinds of pitch lengths, that is, 36.77
mm, 43.77 mm, and 50.33 mm. In the equal-pitch arrangement, all
pitch lengths are fixed to 43.39 mm.
[0036] As shown in FIG. 3, by adopting the 56-pitch variable
arrangement, compared to the equal-pitch arrangement and the
3-pitch variable arrangement, frequencies of pitch noises can be
dispersed and hence, a maximum level of the pitch noises can be
lowered. In the equal-pitch arrangement, a peak of a primary
component in the vicinity of 500 Hz and a peak of a secondary
component in the vicinity of 1 kHz are completely separated from
each other. On the other hand, in the 56-pitch variable
arrangement, due to the dispersion of the respective peaks, a
maximum level of the pitch noises is lowered and, further,
superposition of a dispersed primary component and a dispersed
secondary component is suppressed and hence, the increase of a
noise level caused by the combination of both the primary component
and the secondary component can be suppressed. In this manner,
according to this embodiment, the large variable number is set
while setting the large variable ratio within a range that the
n-order component and the 2n-order component of the noise pitch do
not agree with each other and hence, a noise level can be
remarkably lowered.
[0037] In the above-mentioned embodiment, the pitch variable
arrangement is adopted where in all of the plurality of land
portion rows 18 formed on the tread portion 10, the number of kinds
k of pitch lengths P in the tire circumferential direction CD is
set to N/4 or more and N or less, and a relationship of
P.sub.m-1/P.sub.m<1.050 and a relationship of
1.60.ltoreq.P.sub.1/P.sub.k<2.00 are satisfied. However, such a
pitch variable arrangement may be adopted in at least one land
portion row 18 formed on the tread portion 10. For example, the
above-mentioned pitch variable arrangement may be adopted only in
the shoulder land portion row where problems are liable to occur in
noise pitches, and conventional 3-kinds or 5-kinds pitch variable
arrangement or the equal-pitch arrangement may be adopted in other
land portion rows.
[0038] In the above-mentioned embodiment, all of the plurality of
land portion rows 18 formed on the tread portion 10 adopt the same
pitch variable arrangement. That is, in all land portion rows 18,
the orders of arrangements (arrangement patterns) of the respective
elements 20 having the plural kinds k of pitch lengths P in the
tire circumferential direction CD are set to the same order of
arrangement. However, order of arrangement may differ depending on
the land portion row 18. That is, in at least one land portion row
out of the plurality of land portion rows 18, the arrangement of
the elements 20 having the plural kinds k of pitch lengths P may
differ from the arrangement of the elements of other land portion
rows. For example, by setting the different arrangement order of
the elements in the circumferential direction for the respective
land portion rows 18 while adopting the same kind of the pitch
lengths P in all land portion rows 18, the pitch variable
arrangements of the respective land portion rows 18 may differ from
each other. In this manner, by adopting the different pitch
variable arrangement depending on the land portion row 18, the
respective land portion rows 18 are brought into contact with a
ground at different timings and hence, the frequencies of the pitch
noises can be dispersed at random thus effectively lowering a noise
level.
[0039] As shown in FIG. 2, in the above-mentioned embodiment, the
plurality of land portion rows 18 are respectively displaced from
each other in phase of the elements 20 in the tire circumferential
direction CD. As one example, in FIG. 2, the phase difference
.alpha. between the left shoulder land portion row 18S and the
mediate land portion row 18M disposed adjacently to the left
shoulder land portion row 18S is shown. By displacing the land
portion rows 18 in phase of the elements 20 in the tire
circumferential direction from each other as described above, the
land portions 16 of the respective land portion rows 18 are brought
into contact with a ground at different timings and hence,
frequencies of pitch noises can be further dispersed thus lowering
a noise level. It is unnecessary that all of the plurality of land
portion rows 18 are displaced from each other in phase. At least
one land portion row 18 out of the plurality of land portion rows
18 may differ from other land portion rows 18 in phase of the
elements 20 in the tire circumferential direction CD.
[0040] In the above-mentioned embodiment, the number of pitches N
is set equal in all of the plurality of land portion rows 18.
However, the number of pitches may differ depending on the land
portion row 18. That is, at least one land portion row 18 out of
the plurality of land portion rows 18 may differ from other land
portion rows 18 in the number of pitches. With such a
configuration, frequencies of noises determined based on the number
of pitches can be dispersed.
Second Embodiment
[0041] Although a pneumatic tire according to a second embodiment
basically has the same tread pattern as the pneumatic tire
according to the above-mentioned first embodiment (see FIG. 1), the
pneumatic tire according to the second embodiment differs from the
pneumatic tire according to the first embodiment with respect to
the number of kinds of pitch lengths and a method of setting the
number of kinds of pitch lengths. Hereinafter, the detailed
description is made by focusing on a point which makes the second
embodiment different from the first embodiment while assuming that
factors which are not particularly described have substantially the
same configurations as the first embodiment.
[0042] As shown in FIG. 1 and FIG. 4, in the second embodiment,
each land portion row 18 is formed by arranging repetitive elements
20 each of which is formed of a land portion 16 and a transverse
groove 14 in the tire circumferential direction CD, and the number
of pitches N over the whole circumference of a tire is set equal in
all land portion rows 18. Accordingly, assuming the number of land
portion rows 18 as L, a tire includes N.times.L pieces of the
elements 20 as a whole.
[0043] The number of pitches N over the whole circumference of the
tire in each land portion row 18 is set in substantially the same
manner as the first embodiment and may be set to 30 to 100 or 40 to
80, for example. In this embodiment, the number of pitches N is set
to 56 (N=56). The number of land portion rows L is preferably set
to an integer of 2 to 6, and is more preferably set to an integer
of 3 to 5. In this embodiment, the number of land portion rows L is
set to 5 (L=5). In substantially the same manner as the first
embodiment, a tire circumferential length of the above-mentioned
element 20 is assumed as a pitch length P.
[0044] In the second embodiment, by imparting a plurality of
different pitch lengths P to the elements 20 in five land portion
rows 18, land portion rows each having a pitch variable arrangement
are formed. To be more specific, each land portion row 18 includes
the elements 20 having the plural kinds of pitch lengths P and is
formed by arranging such elements 20 in the tire circumferential
direction CD. Further, not only within each land portion row 18 but
also between the land portion rows 18, the above-mentioned elements
20 have the different pitch lengths P. That is, at least one land
portion row 18 includes the elements 20 which differ in pitch
length P from the elements 20 of other land portion rows 18.
[0045] In the second embodiment, the number of kinds j of pitch
lengths P (that is, variable number) in the whole tread portion 10
are set to N/4 or more and N.times.L or less
(N/4.ltoreq.j.ltoreq.N.times.L). The number of kinds j of the pitch
lengths P is set to N/4 or more and hence, frequencies of pitch
noises are dispersed so that an effect of lowering a noise level
can be enhanced. From a viewpoint of such a noise level lowering
effect, it is preferable that the number of kinds j of the pitch
lengths P be as many as possible. Accordingly, it is preferable
that the number of kinds j be N.times.L/4 or more, it is more
preferable that the number of kinds j be N.times.L/2 or more, and
it is further more preferable that the pitch length P be changed
with respect to all elements 20, that is, j=N.times.L.
[0046] In the example shown in FIG. 4, the pitch length P is
changed with respect to all elements 20 in the tread portion 10,
that is, the number of kinds j of the pitch lengths P are set equal
to the number of pitches N.times.L (j=N.times.L). FIG. 5A to FIG.
5E are views showing the respective land portion rows 18 shown in
FIG. 4 in an exploded manner, wherein all pitch lengths Pc.sub.1,
Pc.sub.2, Pc.sub.3, Pc.sub.4, Pc.sub.5, Pc.sub.6, Pc.sub.7,
Pc.sub.8, Pc.sub.9, Pc.sub.10, . . . , Pc.sub.NL-9, Pc.sub.NL-8,
Pc.sub.NL-7, Pc.sub.NL-6, Pc.sub.NL-5, Pc.sub.NL-4, Pc.sub.NL-3,
Pc.sub.NL-2, Pc.sub.NL-1, and Pc.sub.NL of N.times.L pieces of
elements 20 existing on the tread portion 10 are set to different
pitch lengths.
[0047] In the second embodiment, in the whole tread portion 10,
assuming the number of kinds of pitch lengths P as j and the pitch
lengths P in a descending order as P.sub.1, P.sub.2, . . . ,
P.sub.j, a relationship of P.sub.t-1/P.sub.t<1.050 and a
relationship of 1.60.ltoreq.P.sub.1/P.sub.j<2.00 are established
(in this relationship, t being an integer of 2 to j).
[0048] In this manner, by setting a variable ratio P.sub.1/P.sub.j
which is a ratio of a maximum pitch length P.sub.1 to a minimum
pitch length P.sub.j to less than 2.00, it is possible to suppress
the occurrence of a phenomenon that an n-order component and a
2n-order component of the noise pitch agree with each other thus
generating large noises. Further, by setting the variable ratio
P.sub.1/P.sub.j to 1.60 or more, the dispersion of frequencies of
pitch noises can be accelerated. The variable ratio P.sub.1/P.sub.j
is preferably set to 1.80 or more, is more preferably set to 1.90
or more, and is further more preferably set to 1.95 or more.
[0049] By setting a maximum value of the pitch length ratio
P.sub.t-1/P.sub.t to less than 1.050, in the same manner as the
first embodiment, an effect of dispersing frequencies of the pitch
noises can be enhanced in cooperation with the setting of the
variable number and the setting of the variable ratio described
above. The pitch length ratio P.sub.t-1/P.sub.1 is preferably set
to 1.020 or less (that is, P.sub.t-1/P.sub.t.ltoreq.1.020), and is
preferably set to 1.002 or more (that is,
P.sub.t-1/P.sub.t.gtoreq.1.002).
[0050] In the second embodiment, an upper limit (that is, a maximum
value) of a pitch length ratio of the elements 20 disposed
adjacently to each other in the tire circumferential direction CD
is preferably set to less than 1.71. That is, out of two elements
20 disposed adjacently to each other in the tire circumferential
direction CD, assuming a pitch length of the element 20A having a
larger pitch length as P.sub.L and a pitch length of the element
20B having a smaller pitch length as P.sub.S, it is preferable that
an upper limit of a pitch length ratio expressed by P.sub.L/P.sub.S
be less than 1.71 (P.sub.L/P.sub.S<1.71). By defining an upper
limit of the pitch length ratio P.sub.L/P.sub.S of the elements 20
disposed adjacently to each other in the tire circumferential
direction CD as described above, it is possible to suppress
non-uniform wear caused by a rapid change in rigidity of the land
portion 16. From a viewpoint of non-uniform wear resistance
performance, a maximum value of the pitch length ratio
P.sub.L/P.sub.S is further preferably set to less than 1.34 (that
is, P.sub.L/P.sub.S<1.34).
[0051] The arrangement (that is, an arranging method) of the
elements 20 having plural kinds j of pitch lengths P is not
particularly limited. For example, the elements 20 may be arranged
such that the pitch lengths are gradually increased in the tire
circumferential direction in each land portion row. Alternatively,
the elements 20 may be arranged such that the elements 20 having
plural kinds j of pitch lengths P are divided into three groups,
that is, a large pitch length group, a middle pitch length group
and a small pitch length group in a descending order from the
elements 20 having the larger pitch length P, and the elements are
arranged by selecting the elements from the respective groups such
that the elements belonging to the large pitch length group and the
elements belonging to the small pitch length group are not disposed
adjacently to each other in the tire circumferential direction.
With such a configuration, the elements 20 can be arranged in the
tire circumferential direction CD while suppressing the pitch
length ratio P.sub.L/P.sub.S of the elements 20 disposed adjacently
to each other in the tire circumferential direction to a small
value. The allocation of the elements 20 having the plural kinds j
of pitch lengths P to the respective land portion rows 18 may be
performed such that a total length of the pitch lengths over the
whole circumference of a tire is set equal in all land portion rows
18.
[0052] As one example, from the large pitch length group, the
middle pitch length group and the small pitch length group, a
plurality of elements are allocated in the respective land portion
rows 18 in the tire circumferential direction CD in the order of
the elements having a large pitch length, the elements having a
middle pitch length, the elements having a small pitch length, the
elements having a middle pitch length, the elements having a large
pitch length, the elements having a middle pitch length, the
elements having a small pitch length, the elements having a middle
pitch length, the elements having a large pitch length, the
elements having a middle pitch length, the elements having a small
pitch length, and the elements having a middle pitch length thus
arranging the elements such that the pitch lengths of the elements
are smoothly changed in the tire circumferential direction CD, and
are smoothly changed also in the tire width direction WD (see FIG.
1). That is, in each land portion row 18, in an arrangement of the
elements over the whole circumference of the tire, the elements may
be arranged such that a group of a plurality of elements belonging
to the large pitch length group is disposed at three positions over
the circumference, and a group of a plurality of elements belonging
to the small pitch length group is disposed between the groups of
the plurality of elements belonging to the large pitch length group
while interposing a group of a plurality of elements belonging to
the middle pitch length group between the group of the plurality of
elements belonging to the large pitch length group and the group of
the plurality of elements belonging to the small pitch length
group. Further, the elements disposed adjacently to each other in
the tire width direction WD may be arranged by selecting from the
same group.
[0053] According to the second embodiment, as described above, the
large variable number is set while setting the large variable ratio
within a range that an n-order component and a 2n-order component
of the noise pitch do not agree with each other and hence,
frequencies of pitch noises are dispersed so that a peak of pitch
noises can be lowered. Further, by lowering the peak of the pitch
noises, even when a frequency of the pitch noise and a frequency of
an air column tube resonance agree with each other, the increase of
a noise level can be suppressed. Accordingly, a noise level can be
more effectively lowered than ever before.
[0054] FIG. 6 is a graph showing a result of frequency analysis in
area variation with respect to a 280-pitch variable arrangement
(j=N.times.L) which is adopted as one example of pitch variable
arrangement in the second embodiment, and an equal-pitch
arrangement and a 3-pitch variable arrangement which are adopted as
comparison examples. The analysis is performed by substantially the
same method as the above-mentioned first embodiment. The tire size
and a traveling speed are equal to those of the first embodiment.
The tire pattern is set such that, in the 280-pitch variable
arrangement, pitch lengths are changed at an increment of 0.10 mm
within a range of from 29.07 mm to 57.71 mm. Setting of the pitch
lengths in the 3-pitch variable arrangement and setting of pitch
lengths in the equal-pitch arrangement are equal to those of the
first embodiment respectively.
[0055] As shown in FIG. 6, by adopting the 280-pitch variable
arrangement, compared to the equal-pitch arrangement and the
3-pitch variable arrangement, frequencies of pitch noises can be
dispersed and hence, a maximum level of the pitch noises can be
lowered. In the equal-pitch arrangement, a peak of a primary
component in the vicinity of 500 Hz and a peak of a secondary
component in the vicinity of 1 kHz are completely separated from
each other. On the other hand, in the 280-pitch variable
arrangement, due to the dispersion of the respective peaks, a
maximum level of the noise pitches is lowered and, further,
superposition of a dispersed primary component and a dispersed
secondary component is suppressed and hence, the increase of a
noise level caused by the combination of both the primary component
and the secondary component can be suppressed. In this manner,
according to the second embodiment, the large variable number is
set while setting the large variable ratio within a range that the
n-order component and the 2n-order component of the noise pitch do
not agree with each other and hence, a noise level can be
remarkably lowered.
[0056] In the second embodiment, as shown in FIG. 4, the plurality
of land portion rows 18 are respectively displaced from each other
in phase of the elements 20 in the tire circumferential direction
CD. As one example, in FIG. 4, the phase difference .alpha. between
the left shoulder land portion row 18S and the mediate land portion
row 18M disposed adjacently to the left shoulder land portion row
18S is shown. By displacing the land portion rows 18 in phase of
the elements 20 in the tire circumferential direction from each
other as described above, the land portions 16 of the respective
land portion rows 18 are brought into contact with a ground at
different timings and hence, frequencies of pitch noises can be
further dispersed thus lowering a noise level. It is unnecessary
that all of the plurality of land portion rows 18 are displaced
from each other in phase. At least one land portion row 18 out of
the plurality of land portion rows 18 may differ from other land
portion rows 18 in phase of the elements 20 in the tire
circumferential direction CD.
Another Embodiment
[0057] In the above-mentioned first and second embodiments, the
transverse grooves 14 are formed across the respective land portion
rows 18. However, the transverse groove 14 is not limited to a
groove formed across the land portion rows 18, and a groove which
does not completely cross the land portion row 18 and terminates at
an intermediate portion of the land portion row 18 may be adopted
provided that the groove causes a pitch noise. Accordingly, the
land portions 16 may not be blocks completely divided by the
transverse grooves 14 and may be connected to each other at
portions thereof in the tire width direction.
EXAMPLES
First Example
[0058] Pneumatic tires having a tire size of 265/65R17 and a tread
pattern shown in FIG. 1 and FIG. 2 are manufactured (the number of
pitches N over the whole circumference of a tire is 56 (N=56)). In
the examples 1 to 5, the number of kinds k of pitch lengths P
(variable number), a variable ratio P.sub.1/P.sub.k, a maximum
value of P.sub.m-1/P.sub.m, and a maximum value of P.sub.L/P.sub.S
in the respective land portions rows are shown in Table 1, and
these pneumatic tires basically have the same tread pattern.
[0059] To be more specific, the example 1 is a variable arrangement
having 56 kinds of pitch lengths P where the pitch lengths are
changed at an increment of 0.52 mm within a range of from a minimum
pitch length of 29.10 mm to a maximum pitch length of 57.68 mm
(where the increment of the pitch lengths is fixed, and k=N=56),
that is, the example 1 is an example where pitch lengths of all
elements in the tire circumferential direction are changed (the
arrangement is shown in FIG. 1). The examples 2 to 4 are examples
where, compared to the example 1, a minimum pitch length and a
maximum pitch length are changed (an average value of both the
minimum pitch length and the maximum pitch length being equal to
that of the embodiment 1), and the number of kinds k of the pitch
lengths are changed as shown in Table 1. Setting of the respective
pitch lengths is made such that, in the same manner as the example
1, pitch lengths are changed at a fixed increment within a range of
from a minimum pitch length to a maximum pitch length. The example
5 is an example where the arrangement order of the elements is
changed compared to the example 1.
[0060] To be more specific, in the examples 1 to 4, a plurality of
elements are selected from the previously-mentioned large pitch
length group, the middle pitch length group and the small pitch
length group, and the selected elements are allocated in the order
of the elements having a large pitch length, the elements having a
middle pitch length, the elements having a small pitch length, the
elements having a middle pitch length, the elements having a large
pitch length, the elements having a middle pitch length, the
elements having a small pitch length, the elements having a middle
pitch length, the elements having a large pitch length, the
elements having a middle pitch length, the elements having a small
pitch length, and the elements having a middle pitch length thus
arranging the elements such that the pitch lengths of the elements
are smoothly changed in the tire circumferential direction CD. In
the example 5, a plurality of elements are selected from the
above-mentioned large pitch length group, the middle pitch length
group and the small pitch length group, and the selected elements
are allocated in the order of the elements having a large pitch
length, the elements having a middle pitch length, the elements
having a small pitch length, the elements having a large pitch
length, the elements having a middle pitch length, the elements
having a small pitch length, the elements having a large pitch
length, the elements having a middle pitch length, and the elements
having a small pitch length thus arranging the elements such that
the pitch lengths of the elements are steeply changed in the tire
circumferential direction CD.
[0061] Also the comparison examples 1 to 3 basically have the same
tread pattern as the examples. In the comparison example 1, an
equal-pitch arrangement where a pitch length is set to 43.39 mm is
adopted. In the comparison example 2, a 3-pitch variable
arrangement where pitch lengths are respectively set to 32.84 mm,
43.78 mm, and 54.73 mm is adopted. In the comparison example 3, a
5-pitch variable arrangement where pitch lengths are respectively
set to 32.84 mm, 38.31 mm, 43.78 mm, 49.26 mm, and 54.73 mm is
adopted.
[0062] The respective manufactured tires are assembled to rims
having a size of 17.times.8.0 J at an air pressure of 193 kPa and
the tires are mounted on a test vehicle, and noise performance and
non-uniform wear resistance performance of the respective tires are
evaluated. The evaluation method is described as follows. [0063]
Noise performance: An overall value (OAL) when the test vehicle
travels on a noise measuring course at a vehicle speed of 80 km/h
is measured, and the evaluation is indicated by an index with the
result of the comparison example 1 set as the reference (100).
Table 1 shows that the larger the numerical value, the smaller a
noise becomes thus acquiring favorable noise performance. [0064]
Non-uniform wear resistance performance: A toe-and-heal wear amount
of the tire after a vehicle actually travels a prescribed distance
is measured, and the evaluation is indicated by an index with the
result of the comparison example 1 set as the reference (100).
Table 1 shows that the larger the numerical value, the smaller a
toe-and-heal wear amount becomes thus acquiring favorable
non-uniform wear resistance performance.
TABLE-US-00001 [0064] TABLE 1 Comparison Comparison Comparison
Example 1 Example 2 Example 3 Example 1 Example 2 Example 3 Example
4 Example 5 The Number 1 3 5 56 14 28 56 56 of Kinds k of Pitch
Lengths P.sub.1/P.sub.k 1 1.67 1.67 1.98 1.60 1.96 1.67 1.98
Maximum 1.000 1.333 1.167 1.018 1.046 1.035 1.016 1.018 Value of
P.sub.m-1/P.sub.m Maximum 1.00 1.33 1.17 1.32 1.24 1.32 1.26 1.70
Value of P.sub.L/P.sub.S Noise 100 104 105 110 107 109 108 110
Performance Non-uniform 100 97 98 100 100 99 100 95 Wear Resistance
Performance
[0065] The result of the evaluation is shown in Table 1 where, in
the examples 1 to 5, the noise performance is improved compared to
not only the comparison example 1 where the equal-pitch arrangement
is adopted but also the comparison example 2 where the 3-pitch
variable arrangement is adopted and the comparison example 3 where
the 5-pitch variable arrangement is adopted. Further, in the
examples 1 to 4 where the maximum value of P.sub.L/P.sub.S is set
to a small value, the non-uniform wear resistance performance is
also improved compared to the example 5.
Second Example
[0066] Pneumatic tires having a tire size of 265/65R17 and a tread
pattern shown in FIG. 1 and FIG. 4 are manufactured (the number of
pitches N over the whole circumference of a tire is 56 (N=56), and
the number of land portion rows L is 5 (L=5)). In the examples 11
to 16, the number of kinds j of pitch lengths P (variable number)
in the whole tread portion, a variable ratio P.sub.1/P.sub.j, a
maximum value of P.sub.t-1/P.sub.t, and a maximum value of
P.sub.1/P.sub.S are shown in Table 2, and these pneumatic tires
basically have the same tread pattern.
[0067] To be more specific, the example 11 is a variable
arrangement having 280 kinds of pitch lengths P where the pitch
lengths are changed at an increment of 0.10 mm within a range of
from a minimum pitch length of 29.07 mm to a maximum pitch length
of 57.71 mm (where the increment of the pitch lengths is fixed, and
j=N.times.L=280), that is, the example 11 is an example where pitch
lengths of all elements on the tread portion are changed (an
arrangement being shown in FIG. 1). The elements are arranged such
that a plurality of elements are selected from the above-mentioned
large pitch length group, the middle pitch length group and the
small pitch length group, and the selected elements are allocated
in the tire circumferential direction CD in each land portion row
18 in the order of the elements having a large pitch length, the
elements having a middle pitch length, the elements having a small
pitch length, the elements having a middle pitch length, the
elements having a large pitch length, the elements having a middle
pitch length, the elements having a small pitch length, the
elements having a middle pitch length, the elements having a large
pitch length, the elements having a middle pitch length, the
elements having a small pitch length, and the elements having a
middle pitch length thus arranging the elements such that the pitch
lengths of the elements are smoothly changed in the tire
circumferential direction CD as well as in the tire width direction
WD. That is, in each land portion row 18, in an arrangement of the
elements over the whole circumference of the tire, the elements are
arranged such that a group of a plurality of elements belonging to
the large pitch length group is disposed at three positions over
the circumference, and a group of a plurality of elements belonging
to the small pitch length group is disposed between the groups of
the plurality of elements belonging to the large pitch length group
while interposing a group of a plurality of elements belonging to
the middle pitch length group between the group of the plurality of
elements belonging to the large pitch length group and the group of
the plurality of elements belonging to the small pitch length
group. Further, the elements disposed adjacently to each other in
the tire width direction WD are arranged by selecting from the same
group.
[0068] In the example 12, pitch lengths are changed at a fixed
increment within a range of from a minimum pitch length of 33.38 mm
to a maximum pitch length 53.40 mm (where the number of kinds of
pitch lengths is 14 (j=14)), and a variable number in the tire
circumferential direction is set to 3 in all respective land
portion rows. In the shoulder land portion rows on both sides, the
same pitch length is used only with respect to one kind, and
different pitch lengths are set with respect to other kinds.
[0069] The example 13 is an example where pitch lengths are changed
at a fixed increment within a range of from a minimum pitch length
of 29.07 mm to a maximum pitch length of 57.71 mm (where the number
of kinds of pitch lengths is 70 (j=N.times.L/4=70)), and a variable
number in the tire circumferential direction is set to 14 in all
respective land portion rows. The respective land portion rows do
not use the same kind of pitch length.
[0070] The example 14 is an example where pitch lengths are changed
at a fixed increment within a range of from a minimum pitch length
of 29.07 mm to a maximum pitch length of 57.71 mm (where the number
of kinds of pitch lengths is 140 (j=N.times.L/2=140)), and a
variable number in the tire circumferential direction is set to 28
in all respective land portion rows. The respective land portion
rows do not use the same kind of pitch length.
[0071] The example 15 is an example where a minimum pitch length is
set to 32.84 mm, and a maximum pitch length is set to 54.73 mm.
Other factors are set substantially in the same manner as the
example 11. The example 16 is an example where the arrangement
order of the elements is changed compared to the example 11. In the
example 16, a plurality of elements are selected from the
above-mentioned large pitch length group, middle pitch length group
and small pitch length group, and the selected elements are
allocated in the tire circumferential direction CD in the order of
the elements having a large pitch length, the elements having a
middle pitch length, the elements having a small pitch length, the
elements having a large pitch length, the elements having a middle
pitch length, the elements having a small pitch length, the
elements having a large pitch length, the elements having a middle
pitch length, and the elements having a small pitch length thus
arranging the elements such that the pitch lengths are steeply
changed in the tire circumferential direction CD.
[0072] Comparison examples 1 to 3 are equal to the comparison
example 1 to 3 of the first example.
[0073] The respective manufactured tires are assembled to rims
having a size of 17.times.8.0 J at an air pressure of 193 kPa and
the tires are mounted on a test vehicle, and noise performance and
non-uniform wear resistance performance of the respective tires are
evaluated. The evaluation method is equal to the evaluation method
used in the first example.
TABLE-US-00002 TABLE 2 Comparison Comparison Comparison Example
Example Example Example Example Example Example 1 Example 2 Example
3 11 12 13 14 15 16 The Number 1 3 5 280 14 70 140 280 280 of Kinds
j of Pitch Lengths P.sub.1/P.sub.j 1 1.67 1.67 1.99 1.60 1.99 1.99
1.67 1.99 Maximum 1.000 1.333 1.167 1.004 1.046 1.014 1.007 1.002
1.004 Value of P.sub.t-1/P.sub.t Maximum 1.00 1.33 1.17 1.31 1.24
1.32 1.32 1.25 1.70 Value of P.sub.L/P.sub.S Noise 100 104 105 113
107 111 112 109 113 Performance Non-Uniform 100 97 98 100 100 100
100 100 96 Wear Resistance Performance
[0074] The result of the evaluation is shown in Table 2. In the
examples 11 to 16, the noise performance is improved compared to
not only the comparison example 1 where the equal-pitch arrangement
is adopted but also the comparison example 2 where the 3-pitch
variable arrangement is adopted and the comparison example 3 where
the 5-pitch variable arrangement is adopted. Further, in the
examples 11 to 15 where the maximum value of P.sub.L/P.sub.S is set
to a small value, the non-uniform wear resistance performance is
also improved compared to the example 16.
[0075] Although several embodiments have been described heretofore,
these embodiments have been proposed as examples, and are not
intended to restrict the scope of the present invention. These
novel embodiments can be carried out in other various modes, and
various omissions, replacements and changes can be made without
departing from the gist of the present invention. These embodiments
and their modifications fall within the scope and spirit of the
present invention and are included in the scope of the equivalent
of the present invention as set forth in the appended claims.
* * * * *